1. Field of the Invention
The present invention relates generally to radio frequency (RF) transceivers.
2. Background Art
Typically, a power amplifier (PA) is designed to operate at its maximum efficiency for a known nominal load impedance, such as 50 Ohms, for example. However, when used in a wireless terminal, the PA may have to drive a load that varies in impedance over time. When impedance mismatch occurs, forward and reflected signals at the antenna feed point create a voltage standing wave. This reduces power transfer from the PA to the antenna. Conversely, the impedance mismatch at the antenna feed point also reduces the power transfer from the antenna to the receiver and degrades receiver sensitivity.
An antenna tuner is usually placed between the PA and the antenna to reduce impedance mismatch between the PA and the antenna. Conventionally, the antenna tuner is tuned by relying on instantaneous measurements made at the PA output using a power detector. Because of the broadband nature of power detectors, however, these instantaneous measurements are not very accurate (for example, they may capture power from signals being transmitted by nearby transmitters or leaking signals intended for the receiver) and typically vary drastically from one measurement to the next. As such, there is a need for improved techniques for adjusting an antenna tuner used in a wireless terminal.
The present invention will be described with reference to the accompanying drawings. Generally, the drawing in which an element first appears is typically indicated by the leftmost digit(s) in the corresponding reference number.